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This simulation models the perforation of a six-layer harness satin weave Kevlar target (four inches in width) by a 0.44 caliber copper projectile. Credit: Eric Fahrenthold, The University of Texas at Austin Enlarge

We know it's out there, debris from 50 years of space exploration—aluminum, steel, nylon, even liquid sodium from Russian satellites—orbiting around the Earth and posing a danger to manned and unmanned spacecraft.

According to NASA, there are more than 21,000 pieces of 'space junk' roughly the size of a baseball (larger than 10 centimeters) in orbit, and about 500,000 pieces that are golf ball-sized (between one to 10 centimeters).

Sure, space is big, but when a piece of space junk strikes a spacecraft, the collision occurs at a velocity of 5 to 15 kilometers per second—roughly ten times faster than a speeding bullet!

"If a spacecraft is hit by orbital debris it may damage the thermal protection system," said Eric Fahrenthold, professor of mechanical engineering at The University of Texas at Austin, who studies impact dynamics both experimentally and through numerical simulations.

"Even if the impact is not on the main heat shield, it may still adversely affect the spacecraft. The thermal researchers take the results of impact research and assess the effect of a certain impact crater depth and volume on the survivability of a spacecraft during reentry," Fahrenthold said.

Only some of the collisions that may occur in low earth orbit can be reproduced in the laboratory. To determine the potential impact of fast-moving orbital debris on spacecraft—and to assist NASA in the design of shielding that can withstand hypervelocity impacts—Fahrenthold and his team developed a numerical algorithm that simulates the shock physics of orbital debris particles striking the layers of Kevlar, metal, and fiberglass that makes up a space vehicle's outer defenses.